The IEEE 802.15.4 standard supports both physical and Media Access Con-trol (MAC) layers of low rate Wireless Sensor Network (WSNs). However, this stand-ard considers only the ideal linear power consumption, omitting the fact that the diffu-sion principle in batteries shows the nonlinear process when it releases a charge. Thus, this study proposes a technique that improves the performance of the IEEE802.15.4 standard by allowing its MAC to exploit the nonlinear processes of the battery to pro-long the WSN lifetime. To the best of our knowledge, the proposed techniques is the first that considers both the battery status and network latency status through a cross layer model. The performance of the new algorithm has been examined and compared against that of the legacy IEEE 802.15.4 MAC algorithm through extensive simulation experiments. The results show that the new technique reduces significantly the energy consumption and the average end-to-end delay as well.